With continuous expansion of a mobile communication network size, and continuous miniaturization of base stations, the number of network elements that an operator needs to maintain increases rapidly, and maintenance cost also grows gradually. In order to save operating cost, the NGMN organization led by the TMO and the VDF proposed the concept of self-organization network (self-organization network, SON) in December, 2006. The meaning of the SON is to implement automation as much as possible during planning, deployment, and operating and maintenance stages of a mobile communication network. For the convenience of problem study and standardized work, the 3GPP defines a series of use cases (use case) for SON standardization starting from Release 8, and discusses a corresponding solution for each use case. The use case of coverage and capacity optimization (Coverage and Capacity Optimization, CCO) is a major problem of a cellular network.
A factor that influences system coverage and capacity is parameters of a base station antenna (for example, a downtilt and power of the antenna). Changing the downtilt and power of the antenna is a major means of network optimization, while adaptively changing the downtilt and power is a focus of the SON. Interference is another major factor that influences coverage and capacity. In an OFDMA-based system, due to orthogonality of internal resources of a cell, the interference is mainly inter-cell interference. An inter-cell interference coordination (Inter-Cell Interference Coordination, ICIC) technology reduces interference on a cell edge from a neighbor cell through orthogonality of bandwidth used by an edge of the neighbor cell, thereby improving spectral efficiency of the cell edge, and cell coverage. However, bandwidth division decreases reuse of a frequency band, thereby reducing spectral efficiency of the entire cell, that is, the capacity of the cell. Therefore, it is a compromise problem between coverage and capacity. To achieve desirable compromise between the coverage and capacity, in a dynamic ICIC method, ICIC parameters (for example, an overload indication threshold) are adjusted to adapt to distribution of users.
Dynamic fractional frequency reuse (Fractional Frequency Reuse, FFR) and soft frequency reuse (Soft Frequency Reuse, SFR) are two major dynamic ICIC technologies for improving coverage performance by reducing inter-cell interference at present. However, since frequency bands at cell edges are required to be orthogonal, the system capacity is reduced and the spectral efficiency is decreased. Therefore, neither FFR nor SFR can solve the compromise problem between the system capacity and coverage.
In order to further improve performance of cell edge users, based on the FFR/SFR, the cell edge users are further divided into cell center users and cell remote users in the prior art. For the cell remote users, due to the increase of the reuse distance, interference between each other is reduced, and coverage performance is improved. Further division of the cell edge users reduces bandwidth available to the cell center users, and further reduces reuse of the system bandwidth, thereby reducing the system capacity. To achieve optimization of the capacity and coverage at the same time is still a problem to be solved at present.